There is a problem in the subject of this verse since the use of he might imply that Paul went alone, in which case it may be necessary to say “he went with Silas through Syria….”

The phrase strengthening the churches must refer, of course, to the members of the churches and not to the buildings, as might be understood if the term for church refers primarily to the buildings rather than to the congregations. In some languages one may translate this as “causing the believers of the churches to be strong in their faith” or “causing the congregations to be firm in their faith.” (See also 16.5.)

Quoted with permission from Newman, Barclay M. and Nida, Eugene A. A Handbook on The Acts of the Apostles. (UBS Handbook Series). New York: UBS, 1972. For this and other handbooks for translators see here .